1. Field of the Invention
The present invention relates to a sub-mount for mounting a light emitting device and a light emitting device package, and more particularly, to a sub-mount for mounting a light emitting device which enables emission of light having a uniform intensity of illumination from the light emitting device, and a light emitting device package which is capable of having uniform brightness, using the sub-mount.
2. Discussion of the Related Art
Light emitting diodes (LEDs) are well known as semiconductor light emitting devices that convert current to light. A red LED using GaAsP compound semiconductor has been commercially available since 1962, and together with a GaP:N-based green LED, has been a light source in electronic apparatuses, such as image displays.
A wavelength of light emitted from such an LED depends on a semiconductor material used to fabricate the LED. This is because the wavelength of the emitted light depends on a band gap of the semiconductor material representing energy difference between valence-band electrons and conduction-band electrons.
Gallium nitride (GaN) compound semiconductor has been highlighted in the field of high-power electronic devices because it exhibits a high thermal stability and a wide band gap of 0.8 to 6.2 eV. One of the reasons why GaN compound semiconductor has been highlighted is that it is possible to fabricate a semiconductor layer capable of emitting green, blue, or white light, using GaN in combination with other elements, for example, indium (In), aluminum (Al), etc.
That is, it is possible to adjust the wavelength of light to be emitted, using GaN in combination with other appropriate elements. For example, it is possible to fabricate a blue LED useful for optical recording or a white LED to replace a glow lamp.
By virtue of the recent success of growth of InGaN thin film, it has been possible to fabricate high-luminescent green LEDs. In contrast, initially-developed green LEDs were fabricated using GaP. Because GaP is an indirect transition material, there is degradation in efficiency. Thus, the green LEDs fabricated using this material could not practically produce a pure green light.
By virtue of the above-mentioned advantages and other advantages of GaN-based LEDs, the GaN-based LED market has rapidly grown. Also, techniques associated with GaN-based electro-optic devices have rapidly developed since the GaN-based LEDs became commercially available in 1994.
GaN-based LEDs have been developed to exhibit light emission efficiency superior over that of glow lamps. Currently, the efficiency of GaN-based LEDs is substantially equal to that of fluorescent lamps. Thus, it is expected that the GaN-based LED market will grow significantly.
Such an LED is packaged together with other elements. An example of an LED package is illustrated in FIGS. 1 and 2.
The illustrated LED package includes a silicon sub-mount 2, on which an LED 1 is mounted, an aluminum slug 3, a printed circuit board (PCB) 4, and an aluminum heat sink 5.
The silicon sub-mount 2 has metal lines formed on a flat silicon surface, for electrical connection with the LED 1.
The LED 1 is bonded to the sub-mount 2 using a flip chip bonding process. The sub-mount 2 is bonded to a mirror surface of the aluminum slug 3 using an adhesive.
Leads 6a are fixedly mounted to a package body 6. The leads are electrically connected to electrode metal portions of the sub-mount 2 via conductive wires 7, respectively.
The PCB 4 is bonded to the package body 6 using an adhesive, and includes metal lines 4a to which the leads 6a are attached using a welding process. The aluminum heat sink 5 is attached to the PCB 4, in order to allow heat from the PCB 4 to be outwardly discharged via the aluminum heat sink 5.